The present invention relates generally to reactive distillation units in which a chemical reaction and distillation are carried out simultaneously, and more particularly to a random packing structure housing a particulate catalyst component.
It is known to provide a reactive distillation unit for simultaneously carrying out a chemical reaction and multi-stage distillation. Among the advantages recognized in the use of such units are the lower capital costs due to the requirement for less equipment than other conventional two-step processes, and lower operating costs due to the reaction proceeding under more favorable conditions than would otherwise be the case.
Any reaction system in which the preferred temperature range of the reaction either matches or substantially overlaps that for the distillation is potentially suited for reactive distillation. One particular type of system in which reactive distillation is beneficial is in the production of ethers such as methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME) and ethyl tert-butyl ether (ETBE).
The shape of the packing structure used in a reactive distillation tower is a major variable in the performance of the system as the shape of the structure dictates the flow path tortuosity or effective length of the fluid path through the tower which in turn effects the pressure drop and the overall efficiency of the packing.
Several structures are known which provide acceptable conditions in various systems. For example, it is conventional to provide a structured packing having a solid catalyst component retained in screen envelopes so that the catalyst is exposed to a reacting liquid stream during use. It is also known to employ various shaped random packing structures that are provided with cavities within which solid catalyst components are retained for providing a reactive distillation structure for use in reactive distillation processes.
It is an object of the present invention to provide a hollow saddle-shaped packing structure that is filled with a particulate catalyst component such that the resulting structure can be employed in a reactive distillation process.
It is another object of the invention to provide a saddle-shaped packing structure that provides the benefits of known saddle-shaped random packing while at the same time providing a catalyst support system that allows a reacting phase to effectively access the catalyst so that the reaction can proceed to a high level of conversion.
In accordance with these and other objects evident from the following description. of a preferred embodiment of the invention, a hollow, saddle-shaped packing structure comprises a pair of porous outer and inner semi-cylindrical side walls that are spaced from one another to define an interior space, and a particulate catalyst component retained in the interior space between the side walls. In a preferred form of the invention, the structure includes outer and inner saddle-shaped shell elements that are connected together, wherein each element defines one of the side walls, and includes a pair of generally radially opposed, laterally extending flanges.
By providing an apparatus in accordance with the present invention, numerous advantages are realized. For example, in addition to obtaining the same benefits as are obtained by using saddle-shaped random packing structures in conventional distillation processes, the structure of the present invention also provides a means for supporting a solid catalyst component within the bed to simultaneously allow a chemical reaction to take place during distillation. In addition, the unique saddle shape of the structure permits the void volume of the packing to be varied by varying the size of saddle-shaped structures used in the packing; a feature that is not duplicated in the use of spherical or cylindrical random packing structures. As such, the capacity of the bed and the change of pressure experienced during a reactive distillation process can be adjusted to maximize the separation efficiency thereof.